Figure 3
From: Continuous eclogite melting and variable refertilisation in upwelling heterogeneous mantle
Hybridisation reactions between eclogitic Res2 partial melts and peridotite in the pseudo-ternary Ol-Qtz-Grt diagram projected from (Di + Jd).
Dark red and dark yellow lines illustrate normative compositions of “reaction-zone lithologies” (RZL) formed by reaction between peridotite and incipient, highly siliceous (dacitic) and higher degree, less siliceous (andesitic to basaltic) Res2 melts at 5 GPa (RZL1) and 3 GPa (RZL2), respectively. This leads to a higher normative garnet/orthopyroxene ratio and more Cr-rich clinopyroxene in RZL2, as 3 GPa Res2 melts are less siliceous and more sodic than 5 GPa Res2 melts (see text; SFigs. 5–6, 10; reactions 1–2; reactions 1–3 in SNotes). The compositional variations within the orthopyroxene RZLs formed at different pressures along an adiabat lie on the Hy-Grt thermal divide and lead to corresponding compositional variations in the transition zone layers (TZ1 and TZ2, i.e. the olivine orthopyroxenite/garnet websterite boundaries that mark the silica-undersaturated reaction zone boundaries between peridotite [harzburgite/lherzolite] and the orthopyroxene-rich RZLs). The resulting melt-depleted residual eclogite zones vary considerably in composition over the pressure and temperature range of interest. The dark grey line expresses the hybridisation reaction of incipient melts of peridotite (+H2O) with solid ‘dry’ residual eclogite Res2. This join Grt-Hy represents a thermal divide of garnet-pyroxene13. Ol, olivine; Qtz, quartz; Coe, coesite; Grt, garnet; Hy, hypersthene; Di, diospide; Jd, jadeite; ss, solid solution; P, peridotite; M, eclogitic melt; RZL, orthopyroxene-rich reaction zone layer; TZ, transition zone layer (i.e. the contact between peridotite and orthopyroxene-rich RZL).
